Electrochemical sensor

ABSTRACT

An electrochemical sensor is provided that includes a housing having an outer wall, a plurality of longitudinal chambers disposed within the outer wall, and a reference chamber housing a reference electrode. Ionic communication between the target fluid and the reference electrode must pass sequentially through each of longitudinal chambers from a first longitudinal chamber to the reference chamber. In this manner, the sensor provides generally a long, tortuous flow path, or salt bridge, between the target fluid and the reference electrode, resulting in a high resistance factor for the sensor.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. application Ser.No. 11/681,787, filed Mar. 5, 2007, which is herein incorporated byreference.

FIELD OF THE INVENTION

The present invention relates generally to electrochemical sensors and,more particularly, to such sensors having a reference electrode and ameasuring electrode for measuring parameters of a target fluid.

BACKGROUND OF THE INVENTION

Electrochemical sensors have long been used to measure properties offluids. Such sensors typically include a measuring electrode assemblyand a reference electrode assembly, both which are electrically coupledto an instrument that senses the difference in electrical potentialbetween the electrodes. In sensors of this kind, the measuring electrodeassembly typically is exposed directly to the target fluid; whereas thereference electrode assembly is immersed in a stable electrolyticsolution, i.e., a reference electrolyte. Sensors of this kind furtherinclude an ion-permeable separator, commonly referred to as liquidjunction or salt bridge, disposed between the reference electrolyte andthe target fluid, to enable a closed circuit between the electrodes.

In use, the measuring electrode generates a potential that varies as afunction of prescribed parameters of the target fluid. The potentialdifference between the measuring electrode and the reference electrodeprovides a basis for measuring the prescribed parameters of the targetfluid. For an accurate reading, the reference electrode must provide astable potential.

The liquid junction plays an important role in achieving and maintaininga stable potential for the reference electrode. Ideally, the liquidjunction should enable ionic communication between the referenceelectrolyte and the target fluid, while otherwise preventing transfer orintermingling of the fluids. Contamination or dilution of the referenceelectrolyte can unduly inhibit performance of the reference electrode,which is of particular concern when used in harsh chemical environments.The ability of the liquid junction to inhibit diffusion of the measuredfluid, and ions therefrom, can be generally referred to as itsresistance factor.

Much attention has been given to designing effective liquid junctionshaving a high resistance factor. Many approaches attempt to establish atortuous path for ions through the junction by confining travel throughrelatively complex structural configurations that incorporate multiplecomponents assembled together. For example, certain approaches includemultiple layers held together with wood dowels. Other approaches utilizelong path salt bridges for ionic communication between the liquidjunction and the reference electrode, which generally require suchsensors to have a relatively large sensor body, including housing lengthand diameter. Current approaches, particularly in industrialapplications, often combine multiple tortuous path junctions connectedby long path salt bridges.

Although generally effective, such approaches are relatively expensiveand time-consuming to manufacture. Moreover, performance of suchapproaches can deteriorate with time.

It should be appreciated that there remains a need for anelectrochemical sensor that addresses these concerns. The presentinvention fulfills this need and others.

SUMMARY OF THE INVENTION

In general terms, the present invention provides an electrochemicalsensor having an outer wall, a plurality of longitudinal chambersdisposed within the outer wall, and a reference chamber housing areference electrode. Ionic communication between the target fluid andthe reference electrode must pass sequentially through each oflongitudinal chambers from a first longitudinal chamber to the referencechamber. In this manner, the sensor provides generally a long, tortuousflow path, or salt bridge, between the target fluid and the referenceelectrode, resulting in a high resistance factor for the sensor.

More particularly, in an exemplary embodiment, the housing furtherincludes a bore for receiving a measuring electrode. The plurality oflongitudinal walls are spaced in a radial manner about the bore,extending between the bore and the outer wall. The intermediatelongitudinal chambers of the plurality of longitudinal chambers havewall apertures disposed at opposing ends thereof, such that ionic flowtravels substantially the entire length of each of the intermediatelongitudinal chambers.

The bore of the housing can further include a neck portion projectingfrom a base wall and terminating in a distal opening proximate to thedistal end of the sensor assembly. The distal opening of the borereceives a proximate portion of a junction plug.

In a detailed aspect of an exemplary embodiment, the housing has anouter member and an inner member disposed within the outer member. Theinner member includes the bore and the plurality of longitudinal walls.Either or both the outer member and the inner member can be formed ofmolded plastic.

In another exemplary embodiment, the housing includes a housing bodyformed of unitary construction. The housing body includes a bore forreceiving a measuring electrode and the plurality of longitudinal walls.The housing body can further include a base wall disposed proximate tothe junction plug. The base wall defines an aperture providing ioniccommunication between the junction plug and a first longitudinal chamberof the plurality of longitudinal chambers.

For purposes of summarizing the invention and the advantages achievedover the prior art, certain advantages of the invention have beendescribed herein. Of course, it is to be understood that not necessarilyall such advantages may be achieved in accordance with any particularembodiment of the invention. Thus, for example, those skilled in the artwill recognize that the invention may be embodied or carried out in amanner that achieves or optimizes one advantage or group of advantagesas taught herein without necessarily achieving other advantages as maybe taught or suggested herein.

All of these embodiments are intended to be within the scope of theinvention herein disclosed. These and other embodiments of the presentinvention will become readily apparent to those skilled in the art fromthe following detailed description of the preferred embodiments havingreference to the attached figures, the invention not being limited toany particular preferred embodiment disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the following drawings in which:

FIG. 1 is a cross-sectional view of a first embodiment of anelectrochemical sensor in accordance with the present invention,depicting a reference electrode disposed within a cavity of a housinghaving an outer member and an inner member.

FIG. 2 is partially exploded view of the electrochemical sensor of FIG.1, depicting selected components in cross section, including the innerand the outer members of the housing.

FIG. 3 is a perspective view of the inner member of the housing theelectrochemical sensor of FIG. 1, with portions of the outer wall inphantom.

FIG. 4 is a cross-sectional view of the inner member, taken along theline 4-4, of the inner member depicted in FIG. 3.

FIG. 5 is a cross-sectional view, similar to FIG. 1, of a secondembodiment of an electrochemical sensor in accordance with the presentinvention, including a housing body of unitary construction.

FIG. 6 is partially exploded view of the electrochemical sensor of FIG.5, depicting components in cross section, including the unitary housingbody, a measuring electrode, an upper seal, a junction plug, and a cap.

FIG. 7 is a cross-sectional view of the unitary housing body of theelectrochemical sensor of FIG. 5, depicting an axial bore for receivingthe measuring electrode and portions of an ionic path.

FIG. 8 is a cross-sectional view, taken along the line 8-8, of theunitary housing body depicted in FIG. 7.

FIG. 9 is a cross-sectional view, taken along the line 9-9, of theunitary housing body depicted in FIG. 7.

FIG. 10 is a cross-sectional view, taken along the line 10-10, of theunitary housing body depicted in FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, and particularly to FIGS. 1 and 2, thereis shown an electrochemical sensor assembly 10, for measuring parametersof a target fluid (not shown), such as ORP or specific ions, e.g., pH orsodium. The sensor assembly 10 includes a measuring electrode 12 (e.g.,glass pH electrode) and a reference electrode 14 coupled to a housing16. The housing includes an outer member 18 and an inner member 20. Thereference electrode is disposed within an electrolyte-filled referencechamber 22, defined by the inner member of the housing. The sensorassembly includes a liquid junction comprising a junction plug 24disposed at a distal end of the housing. The inner member aids indefining a long, tortuous flow path, or salt bridge, between the targetfluid and the reference electrode, requiring ionic flow to travellongitudinally and circumferentially about the housing, resulting in ahigh resistance factor for the sensor.

As best seen in FIGS. 3-4, the inner member 20 includes a generallycylindrical bore 26 configured to receive the measuring electrode 12 andfurther includes a plurality of longitudinal walls 28 radiating from thebore, defining a plurality of longitudinal chambers 30 disposed aboutthe bore. More particularly, the inner member includes eightlongitudinal walls 28(a-h), defining eight longitudinal chambers30(a-h), of which one of the longitudinal chambers 30(h) serves as thereference chamber 22, which includes the reference electrolyte. Theinner member is configured such that ionic flow travels substantiallythe entire length of each longitudinal chamber, as the ionic flowcircumscribes about the bore, passing sequentially through thelongitudinal chambers from the first longitudinal chamber 30(a) to thereference chamber 22.

The longitudinal chambers 30(a-h) are connected via wall apertures32(a-g) defined by the longitudinal walls, with exception to thelongitudinal wall 28(h) between the reference chamber 22 and the firstlongitudinal chamber 30(a). The wall apertures enable ionic flow betweenadjacent longitudinal chambers. The wall apertures of adjacent walls aredisposed on opposing ends of the corresponding longitudinal chamber,requiring ionic flow to traverse the length of the correspondingchamber. Access to the first longitudinal chamber 30(a) is provided by abase aperture 36 defined by the base wall 34 and the wall aperture 32(a)at a proximal end of the first longitudinal chamber. Access to thereference chamber is limited to a single aperture, such that ionic flowterminates at the reference electrode 14.

In this manner, ionic flow traverses substantially the entire length ofeach of the longitudinal chambers, traveling longitudinally andcircumferentially about the housing, from the first longitudinal chamberto the reference chamber 30(h). Different number and spacing of thelongitudinal walls can be used in other embodiments. For example, asensor assembly can include at least three longitudinal walls to inexcess of twenty longitudinal walls, as desired for particularembodiments. Moreover, in other embodiments, separate or additional wallstructure can be used to define the reference chamber.

The inner member 20 of the housing 16 is disposed within the outermember 18 and is aligned with a longitudinal axis L_(o) of the housing.The inner member 20 further includes an outer wall 38 disposed about thelongitudinal walls 28(a-h). The outer wall aids in defining thelongitudinal chambers 30(a-h) and is sized to snuggly contact a sidewall40 of the outer member to inhibit liquid seepage therebetween. Thesidewall of the outer member is generally equidistantly spaced from thebore about the circumference thereof.

Both the outer and the inner members (18, 20, respectively) are formedof molded plastic, such as polypropylene, PP, facilitating ease ofmanufacture and cost-effectiveness. In other embodiments, othermaterials can be used. Some examples of other materials that can be usedinclude polyphenylsulfone PPS, polyvinyl chloride PVC, chlorinatedpolyvinyl chloride CPVC, polyvinyldiflouride PVDF, or other materialsknown in the art having appropriate chemical resistivity for aparticular application.

The sensor assembly 10 further includes an upper seal 42 and a cap 44disposed atop the proximal opening of the outer member 18. The upperseal is positioned above the inner member 20 and configured to engagethe inner member and the sidewall 40 of the outer member 18 to provide afluid tight seal, to confine the reference and bridge electrolytes.

With reference now to FIG. 2, the inner member 20 further includes aneck portion 46 of the bore 26. The neck portion projects from the basewall 34 of the inner member and terminates in a distal opening 48,proximate to the distal end of the sensor assembly 10. The distalopening defines an annular recess sized to receive a first o-ring 50 anda proximate portion 52 of the junction plug 24, to provide a secure sealto guard against contamination stemming from the target fluid or bridgesolution in the stem or cavities. The sensor assembly 10 furtherincludes a second o-ring 54 disposed about a distal portion 56 of thejunction plug to engage the outer member 18 of the housing 16.

The junction plug 24 includes a distal surface 58 that is exposeddirectly to the target fluid and a proximal surface 60 confined withinthe housing 16. The junction plug defines a central passage that enablesthe measuring electrode 12 to contact the target fluid. As mentionedabove, the junction plug is configured to engage the first and thesecond o-rings to ensure that ionic communication travels through thejunction plug, between the distal and the proximal surfaces thereof. Thefirst o-ring is received about a first annular projection 62 defined bythe proximal surface, and the second o-ring is received about a secondannular projection 64 defined by the distal surface.

A relatively small area of the proximal surface 60 is directly exposedto the electrolyte within the housing. In this embodiment, the exposedarea of the proximal surface forms an annular region about the peripheryof the junction plug, defined between the distal opening 48 of the innermember and the sidewall 40 of the outer member 18. In this manner, ioniccommunication between the target fluid and the reference electrolytetravels longitudinally through and radially across the junction plug. Inother embodiments, portions of the junction plug exposed to thereference electrolyte can be provided in other configurations.Additional configurations are discussed in Applicants' co-pending U.S.patent application Ser. Nos. 11/533,989 and 11/564,015, filed Sep. 20,2006 and Nov. 28, 2006, respectively, which are herein incorporated byreference for all purposes.

The junction plug 24 is formed of a unitary construction of porousultra-high molecular weight polyethylene. In other embodiments, othermaterials having suitable characteristics can be used. For example,effective materials include ground glass, ceramic, other porousplastics, and wood. In addition, the liquid junction can be formed ofmultiple components and materials.

As seen in FIG. 1, the sensor assembly 10 defines a separation chamber68 between the junction plug 24 and the base wall 34 of the innermember. In this embodiment, the separation chamber is generallycylindrical and is filled with reference electrolyte, facilitating ionicflow with the housing. In selected embodiments, a plug can be disposedwithin the separation chamber having characteristics of enabling ionicflow, while inhibiting contamination. Exemplary materials for the pluginclude ground glass, ceramic, other porous plastics, and wood.

The outer member 18 includes an inwardly facing flange 66 disposed aboutthe distal opening thereof. The flange is sized such that the junctionplug 24 and the second o-ring 54 can be securely seated in placeproximate to the distal opening to contact the target fluid. The secondo-ring is disposed about the junction plug to engage the sidewall 40 ofthe outer member and the inwardly facing flange 66, providing a secureseal about the plug. The first and the second o-rings ensure ioniccommunication occurs through the tortuous path of the junction plug andnot through micro-gaps between the junction and the sidewall.

With reference again to FIG. 1, the reference electrode 14 is notdirectly exposed to the target fluid; rather it is surrounded by areference electrolyte within the chamber 30(h) defined by the innermember 20 of the housing, enabling the reference electrode to provide astable potential for comparison against the potential of the measuringelectrode. The measuring electrode 12 and a reference electrode 14 areconfigured to be coupled to instrumentation, e.g., amplifier (notshown), to sense the potential difference between the measuringelectrode and the reference electrode. Wires attached to the electrodespass through the cap 44 to couple to the instrumentation.

In use, the end portion of the measuring electrode 12 is exposed to thetarget fluid such that the measuring electrode is electrochemicallycoupled to the target fluid. In the exemplary embodiment, a sensorassembly is configured to detect pH (e.g., a glass pH electrode), havinga flat end. However, other embodiments can be configured to measureother parameters, individual or in combination. For example,oxidation-reduction potential (ORP), using a nobel metal electrode, orother types of specific ions can be measured including, for example,ammonium, bromide, chloride, fluoride, sulfide, nitrate, and sodium. Inaddition, measuring electrodes having various bulb-shaped ends can beused.

Referring again to FIG. 2, during assembly, the junction plug 24 isposition about the distal end of the measuring electrode 12. The firstand the second o-rings (50, 54) are positioned over the junction plug24, as depicted. The inner member 20 is positioned over the measuringelectrode so that the junction plug and the first o-ring is snug withinthe distal opening 48 of the bore 26. This combination is then receivedwithin the outer member 18.

Reference electrolyte is placed into the reference chamber along withthe reference electrode. After appropriate conditioning, an electrolyte(salt bridge) solution is introduced throughout the longitudinalchambers and the junction plug 24. Various types of electrolytes can beused, singly or in combination, such as a potassium chloride/silverchloride (KCl/AgCl) mixture. The salt bridge and the reference solutionmay be hardened or gelled by a variety of agents, including epoxy blendsand gelling agents. This can aid in slowing the ingress of ions from thetarget fluid. Optionally, different electrolytes can be used in thelongitudinal or other chambers. Those skilled in the art will recognizethat various reference systems may be used and that various electrolytescan be used as salt bridges. This invention is not necessarily limitedby any particular reference or salt bridge composition.

Thereafter, the upper seal 42 and the cap 44 are also positioned inplace. Adhesive material can be provided to secure the variouscomponents, as needed. Nonetheless, care should be taken to ensure thatadhesive does not bar or excessively inhibit electrochemicalcommunication between the target fluid and the reference electrode orelectrochemically contaminate the electrodes or electrolytes.

With reference to FIG. 5-6, a second embodiment of a sensor assembly 80is shown, including a housing body 82, a measuring electrode 84, areference electrode 86, and a junction plug 88. In this embodiment, thehousing body is formed of unitary construction, including a bore 90, anouter wall 92, and a plurality of longitudinal walls 94 radiatingaxially between the bore and the outer wall. The longitudinal walls aidin defining a plurality of longitudinal chambers 96 disposed about thebore, of which one of the longitudinal chambers serves as a referencechamber 96(f) for receiving the reference electrode 86.

The sensor assembly 80 further includes an upper seal 98 disposed atopthe longitudinal chambers 96 and a cap 100. The measuring electrode 84and a reference electrode 86 are configured to be coupled toinstrumentation, e.g., amplifier (not shown), to sense the potentialdifference between the measuring electrode and the reference electrode.Wires attached to the electrodes pass through the cap to couple to theinstrumentation.

As best seen in FIGS. 7-10, the housing body 82 includes sixlongitudinal walls 94(a-f), defining six longitudinal chambers 96(a-f).In this embodiment, the reference chamber 96(f) is generallycylindrical. Each of the longitudinal walls defines an aperture 102 thatenables ionic communication between adjacent longitudinal chambers, withexception to the longitudinal wall 94(f) between the reference chamberand the first longitudinal chamber 96(a). For each intermediatelongitudinal chambers 96(b-e), the respective apertures are disposed atopposing ends of the chamber such that ionic communication must travelsubstantially the entire length thereof. Access to the reference chamberis limited to a single aperture. Access to the first longitudinalchamber 96(a) is provided by the base aperture defined by the base wall104 and a base aperture 106 defined by a longitudinal wall at a distalend of the first longitudinal chamber. Accordingly, the housing bodyaids in defining a long, tortuous flow path, or salt bridge, between thetarget fluid and the reference electrode, resulting in a high resistancefactor for the sensor.

The base wall 104 is disposed adjacent to the junction plug 88, suchthat ions must migrate axially through and transverse across thejunction plug to pass through the aperture of the cross member,resulting in an increased effective path length through the junctionplug.

In the exemplary embodiment, the base wall 104 defines a single hollowaperture, the base aperture 106. Preferably, the base wall coversbetween about 50 percent to about 98 percent of the proximal surface ofthe junction plug. In the exemplary embodiment, the base wall coversabout 85 percent of the proximal surface of the junction plug.

Other configurations for the base wall can be used. For example, severalapertures as well as other shapes, e.g., ring, rectangle, and so on, canbe used. Moreover, in other embodiments, the base wall can be attacheddirectly to the proximal surface of the cross member. Various apertureshapes can be combined in a single embodiment. Additional configurationsare discussed in Applicants' co-pending U.S. patent applications,identified above.

The sensor assembly 80 excludes a separation chamber between thelongitudinal chambers and the junction plug, as provided in the firstembodiment, sensor assembly 10. However, other embodiments implementinga unitary housing body can provide a separation chamber, similar to thatin the first embodiment.

In the exemplary embodiments discussed in detailed above, referenceelectrolyte is free to flow among longitudinal chambers. In otherembodiments, porous barriers, e.g., aperture plugs, can be disposed inone or more of the wall apertures to retard contamination, whileenabling ionic flow. Materials for such barriers include, for example,ground glass, ceramic, porous plastics, and wood. For example, in oneapproach, wood plugs or other suitable materials can be place in thewalls apertures disposed adjacent to the proximal end of the innermember. In another approach, plugs can be placed in the longitudinalchambers. Such configurations can increase manufacturing costs but,nonetheless, can be beneficial, particularly in harsh chemicalenvironments.

In addition, in the exemplary embodiments above, the apertures of thelongitudinal walls are oriented generally perpendicular to the walls andextend generally linearly through the wall. In other embodiments, one ormore of the wall apertures can implement alternate configurations. Forexample, wall apertures can be angled relative to perpendicular, can bemulti-angled, or can otherwise have a nonlinear path through thecorresponding wall.

It should be appreciated from the foregoing that the present inventionprovides an electrochemical sensor that includes a housing having anouter wall and a plurality of longitudinal chambers disposed within theouter wall, including a first chamber and a reference chamber. Ioniccommunication between the target fluid and the reference electrodepasses sequentially through each of longitudinal chambers from a firstlongitudinal chamber to the reference chamber. In this manner, thesensor provides generally a long, tortuous flow path, or salt bridge,between the target fluid and the reference electrode, resulting in ahigh resistance factor for the sensor.

Although the invention has been disclosed in detail with reference onlyto the exemplary embodiments, those skilled in the art will appreciatethat various other embodiments can be provided without departing fromthe scope of the invention. Accordingly, the invention is defined onlyby the claims set forth below.

1. An electrochemical sensor, comprising: a housing including a proximalend and a distal end, the distal end configured to be proximate to atarget fluid, thereby defining a longitudinal axis, the housing havingan outer wall that circumscribes the housing, the housing defining aplurality of longitudinal chambers disposed within the confines of theouter wall of the housing in which the longitudinal chambers are alignedwith the longitudinal axis, wherein the housing is configured to enableionic communication to flow between the longitudinal chambers; areference electrode disposed within a reference chamber of the housing;and a junction plug having a first surface configured to contact thetarget fluid and a second surface, the junction plug comprising a porousmaterial that enables ionic flow through the junction plug from thefirst surface to the second surface; wherein ionic communication betweenthe target fluid and the reference electrode within the referencechamber must pass sequentially through the plurality of longitudinalchambers traveling in alternating longitudinal directions from a firstlongitudinal chamber to reach the reference chamber.
 2. Anelectrochemical sensor as defined in claim 1, wherein intermediatelongitudinal chambers of the plurality of longitudinal chambers havewall apertures disposed at opposing ends thereof, such that ionic flowtravels substantially the entire length of each of the intermediatelongitudinal chambers.
 3. An electrochemical sensor as defined in claim1, wherein the housing further comprising a bore for receiving ameasuring electrode, the bore between the proximal end and the distalend of the housing.
 4. An electrochemical sensor as defined in claim 3,wherein a plurality of longitudinal walls are disposed between theplurality of longitudinal chambers and are spaced in a radial mannerabout the bore, extending between the bore and the outer wall.
 5. Anelectrochemical sensor as defined in claim 4, wherein the bore of thehousing includes a neck portion projecting from a base wall andterminating in a distal opening proximate to the distal end of thesensor assembly.
 6. An electrochemical sensor as defined in claim 4,wherein the distal opening of the bore receives a proximate portion ofthe junction plug.
 7. An electrochemical sensor as defined in claim 4,wherein the housing has an outer member and an inner member disposedwithin the outer member, the inner member including the bore and theplurality of longitudinal walls.
 8. An electrochemical sensor as definedin claim 7, wherein the inner member of the housing is formed of moldedplastic.
 9. An electrochemical sensor as defined in claim 4, wherein thehousing includes a housing body formed of unitary construction, thehousing body includes a bore for receiving a measuring electrode and theplurality of longitudinal walls.
 10. An electrochemical sensor asdefined in claim 9, wherein the housing body further includes a basewall disposed proximate to the junction plug, the base wall defines anaperture providing ionic communication between the junction plug and thefirst longitudinal chamber of the plurality of longitudinal chambers.11. An electrochemical sensor, comprising: a housing including aproximal end and a distal end, the distal end configured to be proximateto a target fluid, thereby defining a longitudinal axis, the housinghaving an outer wall that circumscribes the housing, the housingdefining a plurality of longitudinal chambers disposed within theconfines of the outer wall of the housing in which the longitudinalchambers are aligned with the longitudinal axis, wherein the housing isconfigured to enable ionic communication to flow between thelongitudinal chambers, the housing having a base wall coupled to adistal end of the longitudinal chambers, the base wall defining a baseaperture that enable ionic flow into a first chamber of the longitudinalchambers; a reference electrode disposed within a reference chamber; anda junction plug disposed at the distal end of the housing, the plughaving a first surface configured to contact the target fluid and asecond surface in confronting relationship to the base wall, thejunction plug comprising a porous material that enables ionic flowthrough the junction plug from the first surface to the second surface;wherein ionic communication between the target fluid and the referenceelectrode within the reference chamber must pass sequentially throughthe plurality of longitudinal chambers traveling in alternatinglongitudinal directions from the first longitudinal chamber to reach thereference chamber.
 12. An electrochemical sensor as defined in claim 11,wherein the housing further comprising a bore for receiving a measuringelectrode.
 13. An electrochemical sensor as defined in claim 12, whereinthe bore of the housing includes a neck portion projecting from the basewall and terminating in a distal opening proximate to the distal end ofthe sensor assembly.
 14. An electrochemical sensor as defined in claim13, wherein the distal opening of the bore receives a proximate portionof the junction plug.
 15. An electrochemical sensor, comprising: ahousing including a proximal end and a distal end, the distal endconfigured to be proximate to a target fluid, thereby defining alongitudinal axis, the housing having an outer wall that circumscribesthe housing, the housing defining a plurality of longitudinal chambersdisposed within the confines of the outer wall of the housing in whichthe longitudinal chambers are aligned with the longitudinal axis,wherein the housing is configured to enable ionic communication to flowbetween the longitudinal chambers; a reference electrode disposed withina reference chamber of the housing; and a junction plug having a firstsurface configured to contact the target fluid and a second surface, thejunction plug comprising a porous material that enables ionic flowthrough the junction plug from the first surface to the second surface;wherein the housing configured such that ionic communication between thetarget fluid and the reference electrode within the reference chambermust pass sequentially through the plurality of longitudinal chamberstraveling in alternating longitudinal directions with respect toadjacent longitudinal chambers from a first longitudinal chamber toreach the reference chamber.
 16. An electrochemical sensor as defined inclaim 15, wherein intermediate longitudinal chambers of the plurality oflongitudinal chambers have wall apertures disposed at opposing endsthereof, such that ionic flow travels substantially the entire length ofeach of the intermediate longitudinal chambers.
 17. An electrochemicalsensor as defined in claim 15, wherein the housing further comprising abore for receiving a measuring electrode, the bore between the proximalend and the distal end of the housing.
 18. An electrochemical sensor asdefined in claim 17, wherein a plurality of longitudinal walls aredisposed between the plurality of longitudinal chambers.
 19. Anelectrochemical sensor as defined in claim 18, wherein the housingincludes a housing body formed of unitary construction, the housing bodyincludes a bore for receiving a measuring electrode and the plurality oflongitudinal walls.
 20. An electrochemical sensor as defined in claim19, wherein the housing body further includes a base wall disposedproximate to the junction plug, the base wall defines an apertureproviding ionic communication between the junction plug and the firstlongitudinal chamber of the plurality of longitudinal chambers.